1. Field of the Invention
The present invention relates in general to data processing and in particular to circuits, systems and methods for processing data in a one-bit format,
2. Description of the Related Art
Current digital audio systems record data on a compact disk (CD), digital audio tape (DAT) or digital video disk (DVD) in a 24-bit format. During playback, this 24-bit data is typically passed through a 24-bit interpolation filter which smooths the incoming digital samples and increases the data sample rate. A delta-sigma modulator then reduces the number of bits representing each sample, for example from 24-bit samples to 5-bit samples. In doing so, the delta-sigma modulator creates significant quantization noise; however, the delta-sigma modulator has the ability to shift this self-generated noise out of the signal band.
The 5-bit data from the delta-sigma modulator is next thermometer encoded to represent 24 levels. The thermometer encoded data is passed through dynamic element matching logic implementing an algorithm for shaping the noise to account for digital to analog converter (DAC) element mismatch. The DAC which ultimately converts the digital data to analog for eventual presentation to the listener as audio is typically a switched-capacitor circuit that also provides filtering.
The new Sony/Philips 1-bit recording system ("Super Audio CD") stores data from an analog modulator onto the given digital storage media in a 1-bit format. As a result, techniques for converting data in the 1-bit digital format to analog must be developed. This is a non-trivial problem since such factors as filtering out of band noise, gain control through the modulator, and hardware minimization must be considered. Moreover, it is usually a requirement that a dynamic range of -120 dB in the audio band be achieved. The trend has been to use multi-bit DACs to achieve this type of dynamic range, however this compounds the problem of adapting to the 1-bit format.
Given the potential for wide acceptance use of the Sony/Philips 1-bit audio format, and the continuous demand for improved sound quality, circuits, systems and methods for digital to analog conversion of 1-bit audio data are required.